Use the proxy API to proxy web requests. You can use the proxy.onRequest event listener to intercept web requests, and return an object that describes whether and how to proxy them.

The advantage of the proxy.onRequest approach is that the code that implements your proxy policy runs in your extension's background script, so it gets full access to the WebExtension APIs available to your extension (including, for example, access to your extension's storage and networking APIs like dns).

Google Chrome provides an extension API also called "proxy" which is functionally similar to this API, in that extensions can use it to implement a proxying policy. However, the design of the Chrome API is completely different to this API. Because this API is incompatible with the Chrome proxy API, this API is only available through the browser namespace.

To use this API you need to have the "proxy" permission. Also, where you want to intercept requests, you also need host permission for the URLs of intercepted requests.